Infra-Red Decoy Flare

ABSTRACT

The invention provides an infra-red decoy flare comprising a pyrotechnic composition which comprises an extrudable and energetic binder in an amount in the range of from 4-35 wt %, which binder comprises a nitrocellulose, an oxidator in an amount in the range of from 40-80 wt %, a pyrotechnic fuel in an amount in the range of from 15-35 wt %, and a carbon source in an amount of up to and including 10 wt %, all amounts based on total pyrotechnic composition. The invention further provides a process for preparing said infra-red decoy flare.

The present invention relates to an infra-red decoy flare.

In modern warfare infra-red guided missiles are often used against aircrafts such as jet aircraft, transport aircrafts and helicopters. These missiles can be launched from the ground or from, for instance, another aircraft, and they are used to target on and track the infra-red radiation of a certain wavelength range which is emitted by the engine of the target aircraft. In order to provide a defense against such infra-red guided missiles decoy flares are used. Such decoy flares produce infra-red radiation, causing the missile to follow the decoy flare instead of the target aircraft. To deal with such decoy flares more advanced infra-red guided missiles have been developed using seeker systems that are able to recognize a decoy flare and to ignore it. Some of these missiles are equipped with a counter-countermeasures (CCM) system which is, for instance, capable of determining the ratio of a long wavelength infra-red emission and a short wavelength infra-red emission, a so-called colour ratio. In case the detected colour ratio differs significantly from that of the target aircraft the seeker system can recognize this as a countermeasure, as a result of which the missile will ignore the decoy flare and keep tracking the target aircraft.

Hence, effective decoy flares need to produce colour ratios that are similar to those of the target aircrafts in question. A problem with many conventional MTV decoy flares (MTV (Magnesium-Teflon-Viton)) is, however, that they produce mainly short wavelength infra-red emissions, which infra-red emissions differ very much from aircraft infra-red emissions. Efforts have therefore been made to develop decoy flares that generate infra-red colour ratios that are more similar to those of target aircrafts. Boron-based and red phosphorous-based pyrotechnic compositions have, for example, been developed for this purpose, but their performance leaves much room for improvement.

Object of the present invention is to provide improved infra-red decoy flares effectively defending aircrafts against missiles that are equipped with CCM systems.

It has been found that such infra-red decoy flares can be formed from a particular pyrotechnic composition.

Accordingly, the present invention relates to an infra-red decoy flare comprising a pyrotechnic composition which comprises an extrudable and energetic binder in an amount in the range of from 4-35 wt %, which binder comprises a nitrocellulose, an oxidator in an amount in the range of from 40-80 wt %, a pyrotechnic fuel in an amount in the range of from 15-35 wt %, and a carbon source in an amount of up to and including 10 wt %, all amounts based on total pyrotechnic composition.

It has been found that these infra-red decoy flares can be used for effectively defending aircrafts against missiles that are provided with CCM systems.

The Infra-red decoy flares according to the present invention display an excellent burning rate, whereas at the same time their compositions can be easily adjusted to conform to the desired colour ratio.

Another advantage is that their production require less or no solvents and that these solvents have less impact on the environment than the solvents used in conventional production. Additionally, the solvents used has significant advantages in relation to the explosive limits and ignition point.

Yet another and substantial advantage of the present infra-red decoy flares is that the pyrotechnic composition used therein is extrudable, which allows for the very easy and save production of decoy flares in a continuous mode of operation. Additionally, during processing the safety is increased because the pyrotechnic mixture burns less violent due to the presence of the solvent.

The binder to be used according to the present invention is extrudable and energetic. With the term energetic is meant that the binder will decompose exothermically.

Preferably, the extrudable and energetic binder to be used in accordance with the present invention comprises a nitrocellulose. Preferably, the nitrocellulose is a low nitrogen content nitrocellulose. In the context of the present invention a low nitrogen content nitrocellulose is defined as a nitrocellulose having a nitrogen content of less than 11.3% wt %.

The oxidator to be used in the pyrotechnic composition according to the present invention is preferably is selected from the group consisting of KClO₄, KClO₃ and NH₄ClO₄. More preferably, the oxidator comprises KClO₄.

In an attractive embodiment of the present invention the extrudable and energetic binder comprises a nitrocellulose, preferably a low nitrogen content nitrocellulose whereas the oxidator comprises KClO₄.

The pyrotechnic fuel to be used in accordance with the present invention can suitably be selected from the group consisting of terephthalic acid phenolphthalein, phthalic anhydride, benzoyl peroxide, 4-amino benzoic acid, sodium salicylate, potassium salicylate, barium salicylate, strontium salicylate, potassium hydrogen phthalate, sodium hydrogen phthalate, barium hydrogen phthalate, strontium hydrogen phthalate, (i.e. conjugated salts from phthalic acid, isophthalic acid, or terephtalic acid.) benzophenone, dodecane, potassium benzoate, sodium benzoate, barium benzoate, strontium benzoate, 4-nitro benzoic acid, 3-nitro benzoic acid, 5-amino tetrazole, ascorbic acid, sodium di-iso ascorbate, potassium di-iso ascorbate, barium di-iso ascorbate, strontium di-iso ascorbate, L-ascorbic acid, stearic acid, dinitro benzoic acid and potassium dinitro benzoate, sodium dinitro benzoate, barium dinitro benzoate, strontium dinitro benzoate.

The pyrotechnic fuel to be used in accordance with the invention may be applied in liquid form as well as in powder form.

The pyrotechnic fuel to be used in accordance with the present invention is preferably selected from the group consisting of terephthalic acid phenolphthalein, phthalic anhydride, benzoyl peroxide, 4-amino benzoic acid, sodium salicylate, potassium hydrogen phthalate, benzophenone, dodecane, potassium benzoate, 4-nitro benzoic acid, 3-nitro benzoic acid, 5-amino tetrazole, ascorbic acid, sodium di-iso ascorbate, L-ascorbic acid, stearic acid, sodium benzoate, dinitro benzoic acid and potassium dinitro benzoate. The pyrotechnic fuel may be applied in liquid form as well as in powder form.

More preferably, the pyrotechnic fuel is selected from the group consisting of potassium dinitrobenzoate, terephthalic acid, sodium salicylate, sodium di-isoascorbate, 3,5-dinitrobenzoic acid, 4-aminobenzoic acid, L-ascorbic acid, ascorbic acid, and sodium benzoate. Most preferably, the pyrotechnic fuel comprises potassium dinitrobenzoate, terephthalic acid, sodium salicylate or sodium-D ascorbate,

In a particularly attractive embodiment of the present invention, the extrudable and energetic binder comprises a nitrocellulose, preferably a low nitrogen content nitrocellulose, whereas the oxidator comprises KClO₄, and the pyrotechnic fuel comprises potassium dinitrobenzoate or sodium-D ascorbate. Such a particular combination of components provides a pyrotechnic composition which displays a most attractive performance when used in an infra-red decoy flare.

The carbon source to be used in accordance with the present invention may comprise lampblack, soot, graphite, charcoal coal, or for those skilled in the art functionally equal materials. Preferably, the carbon source comprises lampblack or graphite Most preferably, the carbon source comprises lampblack.

In the pyrotechnic composition to be used in accordance with the present invention the extrudable and energetic binder is present in an amount of 4-35 wt %, based on total pyrotechnic composition. Preferably, the binder is present in an amount in the range of from 10-15 wt %, based on total pyrotechnic composition.

The oxidator is present in the pyrotechnic composition to be used in accordance with the present invention in an amount in the range of from 40-80 wt %, based on total pyrotechnic composition. Preferably, the oxidator is present in an amount in the range of from 40-72 wt %, more preferably in an amount in the range of from 48-61 wt %, based on total pyrotechnic composition.

The pyrotechnic fuel to be used in the present infra-red decoy flares is present in an amount in the range of from 15-35 wt %, based on total pyrotechnic composition. Preferably, the pyrotechnic fuel is present in an amount in the range of from 16-31 wt %, more preferably in an amount in the range of from 17-28 wt %, based on total pyrotechnic composition.

The carbon source is present in the pyrotechnic composition to be used in accordance with the present invention in an amount up to and including 10 wt %, based on total pyrotechnic composition. The chosen amount of carbon source will depend on the performance requirements for the infra-red decoy flare concerned. Preferably, the carbon source is present in an amount in the range of 1 to 5 wt %, based on total pyrotechnic composition.

The pyrotechnic composition to be used in accordance with the present invention may include other conventional components (burn rate modifier, stabilizer, processing additives, flegmatizer, etc.) which are common for those skilled in the art. If present, these components will be present in an amount of less than 10 wt %, based on total pyrotechnic composition.

The present invention also relates to a process for preparing the infra-red decoy flare according to the present invention, wherein an extrudable and energetic binder in an amount in the range of from 4-35 wt %, which binder is a nitrocellulose, an oxidator in an amount in the range of from 40-80 wt %, a pyrotechnic fuel in an amount in the range of from 15-35 wt %, and a carbon source in an amount of up to 10 wt %, all amounts based on total pyrotechnic composition, are mixed, preferably by means of an extruder, and the mixture (extrudate) so obtained is subsequently pressed in the desired form.

Suitably, the process is carried out in the presence of a solvent that is selected from the group consisting of ethanol, or solvents esters such as ethyl acetate, butyl acetate, or alcohols such as isopropanol butanol. Such solvents have the advantage, when compared with conventionally used solvents such as acetone and hexane, that they have a less impact an the environment and that reduce the risk of safety hazards (explosions) considerably. Preferably, the solvent comprises ethanol.

The solvent is suitably present in an amount in the range of from 0 to 20 wt %, based on total pyrotechnic composition. Preferably, the solvent is present in an amount in the range of from 5 to 14 wt %, based on total mixture. It will be understood by the skilled person that said solvent will in essence not be present in the pyrotechnic composition eventually obtained, due to evaporation of the solvent concerned.

Upon release the infra-red decoy flares in accordance with the present invention will be ignited, and they will be burnt at a sufficient rate and produce enough infra-red emission to ensure that the infra-red guided missile is unlocked, and that it will be prevented from locking back onto the trace of the target aircraft.

The infra-red decoy flare in accordance with the present invention may have the form of a cartridge or a pellet. Its design may be conventional. It may, for instance, have the shape of a pellet or cartridge. The outer surface of the pellet or cartridge can suitably provided with grooves so as to establish an improved burning rate. Said grooves can be rectilinear and longitudinal. It should be noted that the shape and the disposition of the grooves can be chosen by the skilled person from a wide range of known possibilities. However, in order to ensure that the infra-red decoy flare will operate effectively it will need to have an aerodynamic shape. Further, it will be understood that the infra-red decoy flare will comprise an ignition means to ignite the pyrotechnic composition.

EXAMPLES Composition 1

11.9% Nitrocellulose (11.3% w/w nitrogen, type NC Chips)

6.7% plasticizer (di-octyl phthalate, C₂₄H₃₈O₄),

52.7% Potassium perchlorate, (Fluka, art 60441)

23.8% K-H-Phtalate, (Sigma P6758)

5.0% carbon (Cabot)

Composition 2

13.0% Nitrocellulose (11.3% w/w nitrogen, type NC Chips)

31.5% Na-D-iso Ascorbate, (Aldrich, art 496332)

54.9% Potassium perchlorate, (Fluka, art 60441)

0.6% Graphite (Lonza)

The respective nitrocellulose, pyrotechnic fuel, and carbon or graphite components of compositions 1 and 2 were premixed and fed into the first solid feeder of the extruder, the second solid feeder contained KClO₄. The extruder was a Theyson Twin Screw Extruder, (co-rotating self wiping, 45 mm, 1305 mm screw length, 29 L/D). The extruder barrel temperature was set at 50° C., at 25 rounds per minute. The ethanol liquid feed was set to obtain 9% (m/m) ethanol. The resulting extruder rods (flares) obtained from the respective compositions 1 and 2 were perforated strands. Their IR emissions were measured using a Nicolet Nexus FTIR spectrometer with MCT-B wide range detector (Mercury Cadmium Telluride) with beamsplitter and spectral range set to 0.9-10 μm. The distance between the FTIR and flare was 21 meter. The relative humidity was 51% and temperature 17.5° C. The infra-red decoy flares prepared from respective compositions 1 and 2 were determined to be both spectrally balanced. 

1. An infra-red decoy flare comprising a pyrotechnic composition which comprises an extrudable and energetic binder in an amount in the range of from 4-35 wt %, which binder comprises a nitrocellulose, an oxidator in an amount in the range of from 40-80 wt %, a pyrotechnic fuel in an amount in the range of from 15-35 wt %, and a carbon source in an amount of up to and including 10 wt %, all amounts based on total pyrotechnic composition.
 2. A composition according to claim 1, wherein the pyrotechnic fuel is selected from the group consisting of terephthalic acid phenolphthalein, phthalic anhydride, benzoyl peroxide, 4-amino benzoic acid, sodium salicylate, potassium hydrogen phthalate, benzophenone, dodecane, potassium benzoate, 4-nitro benzoic acid, 3-nitro benzoic acid, 5-amino tetrazole, ascorbic acid, sodium di-iso ascorbate, L-ascorbic acid, stearic acid, sodium benzoate, dinitro benzoic acid and potassium dinitro benzoate.
 3. An infra-red decoy flare according to claim 2, wherein the pyrotechnic fuel is selected from the group consisting of potassium dinitrobenzoate, terephthalic acid, sodium salicylate, sodium di-isoascorbate, 3,5-dinitrobenzoic acid, 4-aminobenzoic acid, L-ascorbic acid, ascorbic acid and sodium benzoate.
 4. An infra-red decoy flare according to claim 3, wherein the pyrotechnic fuel comprises potassium dinitrobenzoate, terephthalic acid, sodium salicylate or sodium-D ascorbate.
 5. An infra-red decoy flare according to claim 1, wherein the extrudable and energetic binder comprises a nitrocellulose.
 6. An infra-red decoy flare according to claim 5, wherein the nitrocellulose is a low nitrogen content nitrocellulose.
 7. An infra-red decoy flare according to claim 1, wherein the oxidator is selected from the group consisting of KClO₄, KCIO3 and NH4CIO4.
 8. An infra-red decoy flare according to claim 7, wherein the oxidator comprises KICO4.
 9. An infra-red decoy flare according to claim 1, wherein the carbon source comprises lampblack, soot, graphite, charcoal or coal.
 10. An infra-red decoy flare according to claim 1, wherein the extrudable and energetic binder is present in an amount in the range of from 10-15 wt %, based on total pyrotechnic composition.
 11. An infra-red decoy flare according to claim 1, wherein the oxidator is present in an amount in the range of from 40-72 wt %, based on total pyrotechnic composition.
 12. An infra-red decoy flare according to claim 1, wherein the pyrotechnic fuel is present in an amount in the range of from 16-31 wt %, based on total pyrotechnic composition.
 13. An infra-red decoy flare according to claim 1, wherein the carbon source is present in an amount in an amount in the range of from 1 to 5 wt %, based on total pyrotechnic composition.
 14. A process for preparing the infra-red decoy flare according to claim 1, wherein an extrudable and energetic binder in an amount in the range of from 4-35 wt %, which binder is a nitrocellulose, an oxidator in an amount in the range of from 40-80 wt %, a pyrotechnic fuel in an amount in the range of from 15-35 wt %, and a carbon source in an amount of up to 10 wt %, all amounts based on total pyrotechnic composition, are mixed together and the mixture so obtained is subsequently pressed in the desired form.
 15. A process according to claim 14, wherein the mixing is carried out by means of an extruder.
 16. A process according to claim 14, which is carried out in the presence of a solvent which is chosen from the group consisting of ethanol, or solvents esters such as ethyl acetate, butyl acetate, or alcohols such as isopropanol butanol.
 17. A process according to claim 16, wherein the solvent comprises ethanol.
 18. A process according to claim 16, wherein the solvent is present in an amount in the range of from 5 to 14 wt %, based on total mixture. 